First, bring your butter to room temperature. Buttercream can only be prepared with softened butter, neither cold nor too hot (melted butter) will work.

Prepare a stand mixer with a whisk attachment. Alternatively, use your electric hand mixer.

Make the meringue; Add the egg white to the bowl of the stand mixer and start whipping it. After 30 seconds, add either a few drops of lemon juice or ¼ teaspoon of cream of tartar. Then, while the mixer is on, slowly add the 2 tablespoons of sugar. Continue whipping the egg white for 4-5 minutes until shiny, stiff peaks are achieved. This is the most foolproof way to make meringue, but the cream of tartar / lemon juice is just optional.

In the meantime, prepare the sugar syrup by boiling the water and sugar together in a saucepan on medium-high heat for about 5 minutes until the syrup temperature reaches 240F / 116C.

Once the syrup reaches 240F / 116C, immediately remove it from the stove and slowly pour it into the egg white while the mixer is on low speed.

Increase the speed of the mixer and continue whipping the egg white-sugar syrup mixture for about 5 minutes or until the bowl of the mixer is no longer hot.

Once the mixture reaches room temperature, start adding the softened butter tablespoon by tablespoon on medium speed, then turn the mixer back on medium-high speed and whip it for an additional 4 minutes or until the mixture becomes light, fluffy, and increases in volume.

Lastly, add the vanilla extract and salt and continue whipping for another minute until it is smooth and silky.

At this point, the Italian meringue buttercream should have the perfect pipeable fluffy texture, but if, for some reason, it is too thin, place it in the refrigerator for 30 minutes.

Note that the buttercream texture is best when the butter is at the right temperature (room temperature), and the mixture is freshly whipped. I like to use the frosting immediately or store it at room temperature in a piping bag for a few hours. If stored in the refrigerator, you will need to bring it back to room temperature before using it and might need to give it another minute or two to whip in the stand mixer to increase the volume again.